Father Certain in Daughter's Honeymoon Drowning

Gabe and Tina Watson. Scuba Diving accidentABCNews/Newspix / Rex USA
Tina Watson floats motionless in the background while on a scuba diving adventure with her new husband, Gabe Watson, off the coast of Australia. Gabe Watson has been accused of drowning his new bride and will be tried in an Australian court. Inset shows and undated photo of the couple.

As Gabe Watson waits in an Australian jail to defend himself in court against accusations that he killed his new bride on a scuba diving trip in 2003, the woman's father, Tommy Thomas, has no doubts about what happened in his daughter's final moments.

"He had turned off her oxygen," Thomas told "Good Morning America." Like the millions of viewers that saw media reports of the death, Thomas has seen the image of his daughter floating motionless in the water as captured by a tourist's underwater camera. Watson is not in the picture.

VIDEO: Trial begins for a man accused of drowning his wife 11 days after their wedding.Play

"He had held her until she went unconscious, then turned it back on and let her go to the sea bed," Thomas said.

Eleven days after a fairy tale wedding in Birmingham, Ala., in October 2003, 26-year-old Tina Watson and her new husband, Gabe Watson, went on a scuba diving adventure off the coast of Australia. Now, more than five years later, Gabe Watson is charged with her murder and faces a trial in Australia.

Watson voluntarily returned to Australia May 13, was met by his Australian attorney and taken into custody. His first court appearance is scheduled for Friday.

Earlier this month, the lead Australian prosecutor, Brendan Campbell, led a delegation of Australian law enforcement to Birmingham, Ala., to brief the Thompson family on the case and the Australian legal system.

Watson's attorney refused to talk to ABC News but has said his client is not guilty.

Tina Watson's Father Had 'Reservations' About Her Future

It had been Gabe Watson's idea to go scuba diving for the honeymoon, even though Tina Watson just got her license days before the pair departed for the trip.

Thomas said he was happy about the wedding but had "some reservations and fears about the future for her."

"She said that Gabe had told her that if she wanted him to do things that she liked to do, then she needed to do what he liked to do. And he liked to dive," Thomas said.

Gabe Watson, an experienced rescue diver, told authorities that Tina appeared to panic underwater and clutched at his mask, pulling it off his face.

He said she was too heavy to bring to the surface and instead, he went for help as she sank to the bottom of the ocean. One of the dive leaders pulled Tina to the surface, but efforts to resuscitate her failed.

Police Suspect Watson, Prosecutors Bank on Financial Motivation

Police initially became suspicious of Watson when he changed details of his account. An autopsy found no pre-existing medical condition that could have explained his wife's death, and tests showed there was nothing wrong with her diving gear.

"They [the police] had some 16 different versions [of the story] from him alone," Thomas said. "And there were considerable inconsistencies in several of those versions."

Divers re-created the incident as Watson described it for the investigators, who believe he could have saved her.

Prosecutors claim the motive behind the alleged murder was money, according to a 2008 report by ABCNews.com.

According to Australian authorities, Tina Watson told her father that shortly before she and her husband-to-be were married, he asked his then-fiancee to increase her life insurance policy to the maximum and make him the sole beneficiary.

Thomas said his daughter decided to lie to Watson and say she made the changes, according to authorities.

Mysteries at Tina Watson's Grave

When Thomas got the news about his daughter's death, he said, "it brought me to my knees and it was definitely the worst moment of my life."

After the funeral, Thomas' sorrow gave way to confusion and finally outrage when he noticed that flowers began disappearing from her grave. For months, every memento the family left went missing.

Eventually, undercover police captured a video of Watson allegedly using bolt cutters and chopping away flowers to discard them in a nearby ditch.

"I don't know why anyone would do that," Thomas said. "I don't care who they are."

Watson owns the burial plot and refuses to allow the family to put a marker where Tina lays, Thomas said. There is no headstone to mark her grave.

"She loved life so much and she loved people so much, and I think that's why just about everybody that ever met her loved her," Thomas said.

"To us, she is an angel that's watching after us. I just tell her that I love her and I just keep telling her that I'm going to keep going until I can help her rest and be at peace."